The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Cardiac Exercise Studies with Bioelectromagnetic Mapping

Panu Takala

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 17th of November, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-5720-3)   [1459 KB]
Dissertation is also available in print (ISBN 951-22-5719-X)

Abstract

Bioelectric currents in the heart give rise to differences in electric potential in the body and on its surface. The currents also induce a magnetic field within and outside the thorax. Recording of the electric potential on the surface of the body, electrocardiography (ECG), is a well established clinical tool for detecting insufficient perfusion of blood, i.e., ischemia during exercise testing. In a more recent technique, magnetocardiography (MCG), the cardiac magnetic field is recorded in the vicinity of the chest. Despite the clinical significance of the exercise ECG recordings in patients with suspected coronary artery disease (CAD), little is known about the effect of stress in the MCG of healthy subjects and patients with CAD.

Methods for analysing multichannel MCG signals, recorded during physical exercise testing, were developed in this thesis. They were applied to data recorded in healthy subjects to clarify the normal response to exercise in the MCG, and to data of patients with CAD to detect exercise-induced myocardial ischemia. Together with the MCG, spatially extensive ECG, i.e., body surface potential mapping (BSPM) was studied and the exercise-induced alterations in the two mappings were compared.

In healthy volunteers, exercise was found to induce more extensive alterations in the MCG than in the BSPM during the ventricular repolarisation. In patients with CAD, when optimal recording locations were found and evaluated, alterations of the ST segment in the MCG could be used as indicators of ischemia. Also, ischemia was found to induce a rotation of magnetic field maps (MFMs) which illustrate the spatial MCG signal distribution. The MFM orientation could successfully be used as a parameter for ischemia detection. In the BSPM, regions sensitive to ischemia-induced ST segment depression, ST segment elevation, and ST segment slope decrease were identified.

An analysis method was also developed for monitoring the development of the MCG and the BSPM distributions. It enables examination of different features of the MCG and the BSPM signals as a function of time or the heart rate. In this thesis, the method was used for quantifying exercise-induced change in the orientation of MFMs. Adjustment of the orientation change with the corresponding alteration of the heart rate was found to improve ischemia detection by the exercise MCG. When data recorded during the recovery period of exercise testing were evaluated with similar type of analysis methods, the MCG showed better performance in ischemia detection than the simultanously recorded 12-lead ECG.

This thesis consists of an overview and of the following 6 publications:

  1. Takala P, Hänninen H, Montonen J, Mäkijärvi M, Nenonen J, Oikarinen L, Simelius K, Toivonen L and Katila T, Magnetocardiographic and electrocardiographic exercise mapping in healthy subjects. Ann. Biomed. Eng. 29, 501-9 (2001). © 2001 Biomedical Engineering Society. By permission.
  2. Hänninen H, Takala P, Mäkijärvi M, Montonen J, Korhonen P, Oikarinen L, Nenonen J, Katila T and Toivonen L, Detection of exercise induced myocardial ischemia by multichannel magnetocardiography in single vessel coronary artery disease. Ann. Noninv. Electrocardiology 5, 147-57 (2000). © 2000 Futura Publishing Company, Inc. By permission.
  3. Hänninen H, Takala P, Mäkijärvi M, Montonen J, Korhonen P, Oikarinen L, Simelius K, Nenonen J, Katila T and Toivonen L, Recording locations in multichannel magnetocardiography and body surface potential mapping sensitive for regional exercise-induced myocardial ischemia. Basic Res. Cardiol. 96, 405-14 (2001). © 2001 Steinkopff Verlag. By permission.
  4. Takala P, Hänninen H, Montonen J, Mäkijärvi M, Nenonen J, Toivonen L and Katila T, Beat-to-beat analysis method for magnetocardiographic recordings during interventions. Phys. Med. Biol. 46, 975-82 (2001). © 2001 Institute of Physics Publishing. By permission.
  5. Takala P, Hänninen H, Montonen J, Korhonen P, Mäkijärvi M, Nenonen J, Oikarinen L, Toivonen L and Katila T, Heart rate adjustment of magnetic field map rotation in detection of myocardial ischemia in exercise magnetocardiography. Basic Res. Cardiol. Accepted for publication (2001). © 2001 Steinkopff Verlag. By permission.
  6. Hänninen H, Takala P, Mäkijärvi M, Korhonen P, Oikarinen L, Simelius K, Nenonen J, Katila T and Toivonen L, ST segment level and slope in exercise-induced myocardial ischemia evaluated with body surface potential mapping. Am. J. Cardiol. Accepted for publication (2001). © 2001 Elsevier Science. By permission.

Keywords: magnetocardiography, electrocardiography, coronary artery disease, myocardial ischemia

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© 2001 Helsinki University of Technology

Last update 2011-05-26